and Thiel Mountains. Antarctic Map Folio Series, 12:sheet 5. New York, American Geographic Society.

Winkler, H. G. F. 1974. Petrogenests of MetamorphicRocks, 3rd edition. New York: Springer-Verlag. 320p.

Zeck, H. P. 1970. An erupted migmatite from Cerro del Hoya-zo, SE Spain. Contributions to Mineralogy and Petrol-ogy, 26: 225-246.

Rare-earth element geochemistryof volcanic rocks from the

Executive Committee Range,Marie Byrd Land

WESLEY E. LEMASURIERDepartment of GeologyUniversity of Colorado

Denver, Colorado 80202

PHILIP R. KYLEInstitute of Polar StudiesThe Ohio State UniversityColumbus, Ohio 43210

PETER C. RANKINSoil Bureau

Department of Scientific and IndustrialResearch

Lower Hutt, New Zealand

Volcanoes of the Executive Committee Range(1260 W., 760 to 77°S.) were first described byDoumani (1964), and further work has been re-ported by LeMasurier and Wade (in press). Therange is the largest and most petrologically variedvolcanic range in Marie Byrd Land; it includes rep-resentatives of essentially all the rock types presentin the entire petrographic province. Lavas range incomposition from alkali basalt and basanite to inter-mediate compositions such as hawaiite, mugearite,and benmoreite. An extremely wide range of salicrock types, paralleling those in the African riftvalleys, also occur and include phonolite, quartztrachyte, alkali rhyolite, comenditic trachyte,comendite, and pantellerite (figure 1). Strontiumisotope measurements (Halpern, 1970; Jones and

Walker, 1972; LeMasurier and Wade, in press) onbasaltic, intermediate, and some salic lavas are simi-lar, suggesting they are from a mantle-derivedsource and may be comagmatic. However, it is dif-ficult to derive this great variety of oversaturatedand undersaturated salic rocks from the nephelinenormative alkali basalt magma that seems to be theonly primary magma type available in the province.Several combinations of high- and low-pressurepetrologic processes seem to be called for. Rare-earth element (REE) studies of these rocks havefocused on the Executive Committee Range be-cause of the variety of rocks represented and thefact that field and chronologic relations are betterdisplayed here than anywhere else in Marie ByrdLand.

Thirteen lava samples from the Executive Com-mittee Range together with an alkali basalt, basan-ite, phonolite, and pantellerite from other parts ofMarie Byrd Land were analyzed by Dr. Rankin forREE, cesium, barium, hafnium, lead, thorium, anduranium using spark source mass spectrometry.The analytical technique and precision of themethod are given by Howorth and Rankin (1975).REE analyses are plotted normalized to the chon-drite abundances given by Price and Taylor (1973).Interpretation of the results is in progress. Resultsand some preliminary conclusions are discussedbelow.

Basanite (figure 2). The two samples havesimilar chondrite normalized patterns that showa small positive europium anomaly. Compared tothe alkali basalt (figure 3) the basanites are enrichedin REE. The REE distribution of the basanites istypical of undersaturated basaltic magmas, whichare considered to form by partial melting of agarnet peridotite mantle (Kay and Gast, 1973).

Alkali basalt-hawaiite-mugearite-benmoreite (figure3). There is an increase in REE uranium, thorium,and barium through this series of rocks; an excep-tion is benmoreite 23A, discussed separately below.All samples have a positive europium anomaly.Alkali basalt and basanite (see above) generally havesmall positive europium anomalies inherited frompartial melting and fractionation processes operat-ing in the mantle (Kay and Gast, 1973; Sun andHanson, 1975). The europium anomalies in thehawaiite, mugeraite, and benmoreite (50A) prob-ably constitute a feature that in turn was inheritedfrom the alkali basalt parent. The progressive in-crease in REE through the series is consistent withan origin by fractional crystallization from an alkalibasalt parent.

Benmoreite sample 23A has an exceptionally

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48525660646872S10 2 (wt. percent)

Figure 1. Alkalis versusSi0 2 diagram of analyzed

lavas.

0'-44

16

C

U

a)0.

•70•22d41A

62

IIIIII

•54a

71A2Qd

23Ca•24B4%29

42a23A

•48

2A• 4.5c

•.32

10LaCePrNd

264

3)

;5c

,1.If

1OC

SmE GdT DyHoEr

Figure 2. Chondrite nor-Yb malized REE plot of basan-

ite lavas.

ANTARCTIC JOURNAL

Figure 3. Chondrite nor-malized REE plot of alkalibasalt-hawaiite-mugearite-

benmoreite lavas.

I,

a,

-oC0

U 50a,CLE0

'I,

III

5 IIII

La CePrNd SmE GdT D HoEr Y

large positive europium anomaly (EuIEu* = 1.791)and a high barium content. An anomaly of the mag-nitude observed in 23A is unusual and difficult toexplain. The data suggest addition or accumulationof large amounts of feldspar, but the sample isnearly aphyric and shows no evidence of feldsparphenocrysts that could be cumulus in origin. Low-or high-pressure fractionation processes are un-likely to account for the observed europiumanomaly.

Quartz trachyte (figure 4). Two samplesshow extremely different REE patterns. Sample24B has low barium (less than 50 parts per million)and a large negative europium anomaly (EuIEu* =

l EuIEu* = the measured concentration divided by the concen-tration estimated by interpolating the chondrite normalizedsamarium and gadolinium values.

0.37) indicative of feldspar fractionation. The othersample (42A) has an extremely high barium (1,600parts per million) and a small positive europiumanomaly (Eu/Eu* = 1.08); petrogenesis of thissample did not involve feldspar fractionation.

Phonolite (figure 5). Three phonolite sampleshave similar REE patterns except for varying euro-pium contents, and they must have evolved by simi-lar processes. Feldspar fractionation in slightly dif-ferent abundances would account for the varyingnegative europium anomalies. Sample 54A is themost fractionated with the lowest barium, highesturanium, thorium, lead, and largest europiumanomaly, yet it has a total REE content intermediatebetween the other two samples. It may have formedfrom a parent with a lower REE content thansamples 20D and 71A.

Relative to the analyzed alkali basalt and basan-ite, some phonolites show a greater enrichment ofthe heavy REE compared to the light REE. As frac-

December1976 265

1000

500

- 100L)

E

In

5C

10 1III 1111111 I

L CeP rNdSoE0GdT D HoE,Y

Figure 4. Chondrite normalized REE plot of quartz trachytelavas.

- La CoPrNd SmE GdTbDyHoE r Yb

Figure 5. Chondrite normalized REE plot of phonolite lavas.

tionation of most mineral phases present in theselavas will not result in a greater enrichment of theheavy REE compared to the light REE, it appearsthat the phonolites were not derived from a parentlike the analyzed alkali basalt or basanite. A basan-ite with a higher abundance of light REE, or a lowerabundance of heavy REE, would be a suitableparent (compare basanite lavas from the McMurdoSound area) (Sun and Hanson, 1975, 1976; Kyleand Rankin, 1976).

Salic lavas (figure 6). Characteristic of allthese lavas is their variable chondrite normalizedpatterns and their large negative europium ano-malies (EuIEu* ranges from 0.20 to 0.65). Substan-tial quantities of feldspar fractionation must haveoccurred during the formation of these lavas. Theparents and processes of fractionation are underinvestigation.

W. E. LeMasurier collected the samples duringfieldwork supported by National Science Founda-tion grant DPP 70-02980.

References

Doumani, G. A. 1964. Volcanoes of the Executive CommitteeRange, Byrd Land. In: Antarctic Geology and Geophysics(Adie, R. J . , editor). Amsterdam, North Holland PublishingCompany. 666-675.

Halpern, M. 1970. Rubidium-strontium dates and 87Sr/86Srinitial ratios of rocks from Antarctica and South Americaa progress report. Antarctic Journal of the U.S., V(5): 159161.

Howorth, R., and P. C. Rankin. 1975. Multi-element charac-terization of glass shards from strati graphically correlatedrhyolitic tephra units. Chemical Geology, 15: 239-250.

Jones, L. M., and R. L. Walker. 1972. Geochemistry of theMcMurdo volcanics, Victoria Land, part 1. Strontium isotopecomposition. Antarctic Journal of the U.S., VI1(5): 142-144.

Kay, R. W.. and R. W. Gast. 1973. The rare earth content andorigin of alkali-rich basalts. Journal of Geology, 81: 653-682.

Kyle, P. R., and P. C. Rankin. In press. Rare-earth elementgeochemistry of Late Cenozoic alkaline lavas of the McMurdoVolcanic Group, Antarctica. Geochiinica et Cosmochi,nica Acta.

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LeMasurier, W. E., and F. A. Wade. In press. Volcanic historyin Marie Byrd Land: implications with regard to southernhemisphere tectonic reconstructions. In: Proceedings ofthe International Symposium on Andean and Antarctic Vol -canology Problems, Santiago, Chile (0. Gonzalez-Ferran, edi-tor). Rome, International Association of Volcanology andChemistry of Earth's Interior.

Price, R. C., and S. R. Taylor. 1973. The geochemistry of Dune-din Volcano, East Otago, New Zealand: rare earth elements.Contributions to Mineralogy and Petrology, 40: 195-205.

Sun, S. S., and G. N. Hanson. 1975. Origin of Ross Islandbasanitoids and limitations upon the heterogeneity of mantlesources of alkali basalts and nephelinites. Contributions toMineralogy and Petrology, 52: 77-106.

Sun, S. S., and G. N. Hanson. 1976. Rare earth element evi-dence for differentiation of McMurdo volcanics, Ross Island,Antarctica. Contributions to Mineralogy and Petrology,54: 139-155.

La CePrNd Sm E GdTbDyHoEr Yb

Figure 6. Chondrite normalized REE plot of salic lavas.

Igneous rocks of Peter I Island

THOMAS W. BASTIENErnest E. Lehmann Associates

Minneapolis, Minnesota 55403

CAMPBELL CRADDOCKDepartment of Geology and GeophysicsThe University of Wisconsin, Madison

Madison, Wisconsin 53706

Peter I Island lies in the southeastern PacificOcean at 68°50'S. 90°40'W. about 240 nauticalmiles off the Eights Coast of West Antarctica. Ris-ing from the continental rise, it is one of the fewtruly oceanic islands in the region. Few people havebeen on the island, and little is known of its geology.

Thaddeus von Bellingshausen discovered andnamed the island in 1821, and it was not seen againuntil sighted by Pierre Charcot in 1910. A Nor-wegian ship dredged some rocks off the west coastin 1927, and persons from the Norvegia achievedthe first landing in 1929. USNS Burton Islandput a party ashore in Norvegia Bay in 1960; Crad-dock collected 29 rock specimens at that time.

Peter I Island is a glaciated volcanic island about20 kilometers long and 1,750 meters above sealevel. The few rock exposures are mainly in shorecliffs; the narrow beaches contain large clasts ofrock and glacial ice (figure 1). A well-developedmarine platform surrounds the island and inter-rupts the otherwise symmetric profile of a large vol-canic seamount.

The observed bedrock consists of interbeddedflows of basalt and more siliceous lavas; flow thick-nesses are mainly less than 10 meters, and apparentdips are 5 degrees or less. Lavas vary from denseto highly vesicular, and a few surfaces show pahoe-hoe or ropy structure (figure 2). Some trachyan-desite flows contain numerous gabbroid inclusions.Dikes and small stocks cut the stratified rocks. Asingle potassium-argon whole-rock age of 12.5 ± 1.5million years was obtained on a basalt flow fromNorvegia Bay.

Broch (1927) described the 175 dredged rocksand identified three rock types: basalt, andesite,and trachyandesite. Andesite is lacking in the 1960collection, but the trachyandesite from the shorecontains inclusions of gabbroid rocks. Most rocksfrom the island are basalt; other varieties comprisea minor fraction.

The basalts are hypo- to holocrystalline, com-monly porphyritic, and consist of clinopyroxene,intermediate plagioclase, metallic oxides, and oh-

December 1976 267